Question

A uniform plane wave in air impinges normally on a dielectricwall.
The magnitude of the total E fieldmeasured in
front of the wall is shown in Figure P4.9
(a) What is the permittivity of the wall?
assumeμ2=μ0.
(b) What is the frequency of the wave?
Forgot to put the answers the book says:
(a) 9εo
(b) 75MHz